The present invention relates to closure caps for sealing glass or plastic containers and more particularly to an improved composite closure cap having a metal cover and molded plastic container engaging ring. The metal cover and the plastic ring have tapered and engaging surfaces for a controlled closure cap removal torque.
Composite closure caps are well known and are widely used. They include a disc-like cover portion inserted into a circular molded plastic ring with the ring providing threaded or other means for attaching the composite cap to the container. A sealing gasket is provided on the metal cover and tamper indicating means are sometimes provided in the form of a vacuum indicator button on the cover with or without an additional tamper indicating band provided as a portion of the molded plastic ring.
While such composite closures have found acceptance in various packaging uses, including the vacuum packaging of food, prior composite closures have proven unsatisfactory for certain food packages where heat is applied during the sealing operations in retorting and otherwise. A serious drawback to certain of these prior closures has been a significant reduction in torque during the package handling and/or shelf life. The removal torque for the closure cap can become significantly reduced resulting in potential problems with consumer confidence and reduced resistance to abuse. Even where attempts have been made to increase this torque by the application of excess rotational force to the cap during application, the result has been creepage of portions of the plastic ring and container causing a loss of removal torque between the ring and threads and between the ring and the separate closure cover.
An object of this invention is to minimize this drop in removal torque by reducing the force in the plastic threads which cause it.
Other and further objects of the present invention will become apparent upon an understanding of the illustraive embodiments about to be described, or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice.